Bacterial infections affect a wide variety of animals (including humans), threatening their health and safety. For example, mastitis is a highly infectious bacterial infection affecting mammalian mammary glands. It is the most common, and the most costly, disease affecting dairy cows. Mastitis exists in two forms: "clinical," characterized by visually detectable alterations in milk and mammary gland, and "subclinical," where the infection is not directly evident by visual inspection. It has been estimated that at least one-half of the cows in the United States have mastiffs, and most of these infections are subclinical.
Many bacterial pathogens can cause mastitis, including Strep. agalactiae, Staph. aureus, Strep. uberis, Strep. dysgalactiae, E. coli, P. aeruginosa and Klebsiella species. Of these pathogens, Strep. agalactiae and Staph. aureus are associated with infections that arise primarily from contaminated milking equipment. Such infections are known as "contagious mastitis." The other mastiffs infections, known as "environmental mastiffs," primarily result from pathogens that contact the teat during the inter-milking period. These pathogens may be transferred from wind-borne matter, bedding material or ground contaminants, such as soil and manure, that contact the udder when the animal lies down. In all cases, the route of transmission of the pathogen to the inner gland is through the teat orifice.
To prevent mastitis, a variety of disinfecting teat dips have been developed. These disinfectants include iodophors, quaternary ammonium compounds, chlorhexidine, sodium hypochlorite, hydrogen peroxide, organic acids (e.g., capric, lactic, lauric), dodecylbenzene sulfonic acid (DDBSA), and chlorous acid. Several of these materials are very effective in limiting the transmission of contagious mastiffs by destroying the pathogens that contact the teat during, and immediately subsequent to, the milking operation. However, these teat dips do not have sufficient longevity to protect the teat from bacteria that contact the udder during the 8 to 12 hour inter-milking period, particularly in inclement weather and when the animal lies down.
A few longer-lasting protective compositions have been developed that reduce the incidence of environmental mastitis, but these compositions have inherent practical problems in both application and maintenance. For example, a non-germicidal acrylic latex teat dip, which dries as a protective film over the teat end and remains intact until the following milking, significantly reduces the possibility of acquiring certain infections. However, other infections may be fostered by its application, since bacteria tend to propagate in the moist region between the skin and such latex coatings. This can irritate the dermal layer and act as a conduit for the transfer of organisms to the teat orifice. Furthermore, the acrylic latex dip is inconvenient for dairy herders who must physically strip the latex from each teat prior to milking the animal. Despite the addition of germicides to alleviate the skin irritation, the acrylic latex dip has not proven to be commercially viable since inconvenience, incomplete action, and expense have remained prevalent and insurmountable problems.
A more successful composition for preventing mastitis is disclosed in U.S. Pat. No. 4,891,216. That patent is directed to a disinfecting composition in which longevity is achieved using a gelling agent formed from the polymerization of the monomer 2-acrylamido-2-methylpropane sulfonic acid ("polysulfonic acid"). This polysulfonic acid gelling agent is compatible with the metastable chlorous acid disinfecting system of U.S. Pat. No. 4,986,990, and forms a protective film over the teat end which limits the passage of contaminating environmental pathogens into the teat during the inter-milking period. This composition has been proven effective in field studies and is widely accepted by consumers for prevention of mastitis, and is sold under the name UDDER-GOLD (Alcide Corporation, Redmond, Wash.).
However, in spite of the many positive attributes of the disinfecting composition of U.S. Pat. No. 4,891,216, the strong affinity of the polysulfonic acid gelling agent to the dermal layer has proven problematic. Specifically, the polysulfonic acid film has a tendency to form a stubborn solid matrix at the teat end, especially when teat dip residues from prior applications have not been thoroughly washed off. Thus, after a series of successive post-milking applications accompanied by only partial removal of the residual film, the dairy herder is faced with a hard deposit at the teat end. Physical removal of the deposit can result in skin irritation and possibly removal of dermal tissue. The resulting sore areas and lesions cause significant discomfort during milking, particularly when vacuum milkers are used. In addition, when the polysulfonic acid gelling agent is combined with a metal chlorite (which, in combination with a suitable acid, generates the metastable chlorous acid disinfecting system), a high level of salts is produced. Such salts are potentially irritating to the teat skin when the solution dries to a hyperosmotic state.
Furthermore, manufacture of the disinfecting composition of U.S. Pat. No. 4,891,216 is complicated by the use of the polysulfonic acid gelling agent. Polysulfonic acid is commercially available only as a highly viscous aqueous solution (ca. 16% solids) with a pH.ltoreq.1 (e.g., HSP-1180 from Henkel Corporation). As a result, manufacture of the disinfecting composition requires a preheating step to soften the polysulfonic acid, as well as high pressure to transfer the aqueous polymer to a mixing container. In addition, the polysulfonic acid polymer is difficult to use in the protic acid component of the disinfecting composition. Because of the high acidity of the polysulfonic acid polymer, it is difficult to precisely adjust the pH of a partially neutralized solution of polysulfonic acid and a protic acid so that the pH of the final composition is reproducible. Such predictability is required for uniformity of action since the concentration of chlorous acid in the disinfecting composition is critically dependent on the pH. The irreproducibility of pH when polysulfonic acid is used as the gelling agent substantially increases the cost of manufacture, and ultimately, the finished product.
Thus, there is a need in the art for a suitable disinfecting composition which will surmount the problems identified above. More specifically, there is a need in the art for a long-lasting disinfecting composition which will adhere to surfaces in an acceptable manner, that is easy to handle and manufacture, and that provides a readily-removable anti-microbial protective layer. The present invention fulfills these needs, and provides further related advantages.